Utilizing luminance variation of the white area of the tone chart in tone correction

Abstract

An image forming apparatus outputs a tone chart for calibration by a printer, reads the output tone chart by a scanner, determines whether data on a sheet is affected by a surface shape of the sheet based on the read tone chart, corrects data on a white area of the read chart based on a result of the determination, and executes calibration using the corrected data.

What is claimed is: 
     
       1. An image forming apparatus comprising:
 an output unit configured to output a tone chart including a white area; 
 a reading unit configured to read the tone chart output by the output unit; 
 a determination unit configured to determine variance of luminance of the white area of the tone chart read by the reading unit; 
 a luminance value correction unit configured to correct a luminance value of the white area of the tone chart read by the reading unit based on a result of the determination made by the determination unit; and 
 a tone correction unit configured to perform tone correction using the luminance value of the white area corrected by the luminance value correction unit. 
 
     
     
       2. The image forming apparatus according to  claim 1 ,
 wherein the determination unit is configured to determine the variance of the luminance for each of color planes of red (R), green (G), and blue (B). 
 
     
     
       3. The image forming apparatus according to  claim 1 ,
 wherein the determination unit is configured to determine the variance of the luminance using a histogram for the white area. 
 
     
     
       4. The image forming apparatus according to  claim 3 ,
 wherein the determination unit is configured to determine the variance of the luminance using a distance between a peak luminance value and a highly-frequent luminance value in the histogram for the white area. 
 
     
     
       5. The image forming apparatus according to  claim 1 ,
 wherein the determination unit is configured to use an average value of the luminance of the white area. 
 
     
     
       6. The image forming apparatus according to  claim 1 ,
 wherein the determination unit is configured to use a variance value of the luminance of the white area. 
 
     
     
       7. The image forming apparatus according to  claim 1 ,
 wherein the luminance value correction unit is configured to correct the luminance value of the white area based on a luminance value of an area other than the white area. 
 
     
     
       8. The image forming apparatus according to  claim 1 ,
 wherein the luminance value correction unit is configured to correct the luminance value of the white area based on a luminance value of an area other than a highlight area. 
 
     
     
       9. The image forming apparatus according to  claim 1 ,
 wherein the luminance value correction unit is configured to acquire previously associated paper white information using a histogram for the white area or the variance of the luminance of the white area. 
 
     
     
       10. A control method of an image forming apparatus, the method comprising:
 outputting a tone chart including a white area; 
 reading the output tone chart; 
 determining variance of luminance of the white area of the read tone chart; 
 correcting a luminance value of the white area of the read tone chart based on a result of the determining; and 
 performing tone correction using the corrected luminance value of the white area.